Search Results (491)

To solve the problems of poor weld formation, difficult slag removal, and inferior joint microstructure and hardness in conventional narrow-gap submerged arc welding (NG-SAW), a swing arc NG-SAW process assisted by pre-embedding cold wires was proposed. Synergistically optimizing the welding energy parameters and additional cold wires ensured sound weld formation and enhanced slag detachability, while the efficiency of multilayer welding was improved by reducing the number of weld layers by 33.3%. The slag adhesion mechanism is clarified as follows: a high welding heat input facilitates elemental diffusion at the weld–slag interface, leading to the formation of a continuous and thick interlayer composed of (Fe,Mn)O and MgO-Al₂O₃-CaO phases. This interlayer strengthens the chemical bonding between slag and weld, thereby impeding slag removal. Microstructure evolution analysis of the multilayer welded joint revealed that the variable-angle design increases the groove volume and, combined with the heat-absorbing effect of the additional wires, accelerates molten pool cooling, thereby refining grains in both the weld metal zone and reheat-affected zone. Meanwhile, the tempering exerted by the heat-affected zone (HAZ) of the subsequent weld layer on the previous layer is attenuated. This promotes the gradual transformation of hard-brittle lath martensite in the coarse-grained heat-affected zone (CGHAZ) of the bottom layer into tougher tempered martensite/bainite in the CGHAZ of the upper layers. As a result, the hardness uniformity within the HAZ, the critical weak region of the joint, was enhanced by 54%, enabling synchronous improvement in microstructural homogeneity, hardness distribution, and overall welding efficiency. Full article

Vacuum arc remelting (VAR) is essential for producing premium titanium alloys, where an externally applied alternating magnetic field enables circumferential stirring to control ingot homogeneity. However, current magnetic field parameter design relies on empirical trial-and-error approaches, lacking systematic theoretical guidance. To address this issue, this study establishes a comprehensive multi-physics framework through a two-dimensional axisymmetric swirl model integrating electromagnetic, fluid dynamics, thermal, and solute transport phenomena. Our findings demonstrate that both the magnetic field strength and period exhibit optimal operating ranges, which directly influence ingot homogeneity. As magnetic field strength increases progressively, ingot uniformity shows a distinctive non-monotonic response—initially improving before subsequently deteriorating. Correspondingly, with increasing stirring period, macrosegregation undergoes a distinct three-stage evolution: initial mitigation, subsequent aggravation, and final alleviation. These phenomena originate from the small-scale circulatory flow generated by the external magnetic field on the surface of the VAR molten pool. The interactions among the flow, the solute diffusion layer, and the mushy zone collectively alter elemental diffusion behavior, ultimately determining the homogeneity of the ingot. This study provides a theoretical foundation for precise control of ingot homogeneity in titanium alloy VAR processes and demonstrates significant potential for engineering applications. Full article

To improve the surface properties of 40Cr steel, Ni45/Y₂O₃ laser-cladded coatings (L-CCs) were fabricated on the surface of 40Cr steel. The effects of Y₂O₃ addition (0.5%, 1.0%, and 1.5%) on the microstructure, microhardness, residual stress, wear resistance, and corrosion resistance of the L-CCs were systematically investigated. The results indicate that Y₂O₃ has a significant effect on enhancing the corrosion resistance and suppressing the residual stress of the L-CCs, whereas its contribution to the improvement of microhardness and wear resistance is relatively limited. Compared with the single Ni45 L-CC, the L-CC containing 1.0% Y₂O₃ exhibited a 45.9% reduction in corrosion current density and a 79.3% reduction in residual stress. At a Y₂O₃ addition of 0.5%, the microhardness increased by 4.0%, while the average friction coefficient and wear mass loss decreased by 4.8% and 2.6%, respectively, relative to the single Ni45 L-CC. Excessive Y₂O₃ addition reduces the fluidity of materials in the molten pool and deteriorates the microstructural uniformity, thereby weakening or even impairing the surface properties of the L-CCs. Full article

The crack-free welding of aluminum alloy is very significant in manufacturing lightweight components since aluminum alloys are susceptible to solidification cracking during welding. This work reviews the current understanding and advancements in the study of solidification cracking during welding aluminum alloys. Solidification cracks typically form near the end of the solidification process within the mushy zone, a region behind the molten pool where the material is partially solid and partially liquid. The complex high-temperature metallurgical behaviors in this zone play a crucial role in crack initiation. Research on the cracking resistance of filler materials has progressed significantly, offering valuable insights for mitigating cracks. The review covers the mechanisms of solidification cracking, influencing factors, and the cracking resistance of filler materials. It also highlights future research directions to deepen the understanding of metallurgical mechanisms and to support practical engineering solutions for controlling solidification cracks in welding aluminum alloys. Full article

A 2D multiphase-flow coupling simulation model for preparing nanocrystalline ribbons using planar-flow casting (PFC) with a cooling roller was established. The influence of roller speed on molten pool characteristics, cooling-roller heat transfer, and ribbon thickness was analyzed. The effect of ribbon thickness on the total loss and permeability of the magnetic cores was investigated. The results indicate that the molten pool size decreased as the roller speed increased. At t = 5 ms, the maximum heat-transfer coefficient of the roller surface increased from 2.09 × 10⁶ W·m⁻²·K⁻¹ at 15 m/s to 2.6 × 10⁶ W·m⁻²·K⁻¹ at 24 m/s. The ribbon thickness decreased from 39.96 μm to 20.02 μm (a 49.9% reduction) as the roller speed increased from 18 m/s to 30 m/s. The total loss of the nanocrystalline magnetic cores increased with ribbon thickness, whereas their permeability increased as ribbon thickness decreased. At 100 kHz, the nanocrystalline magnetic core made of 10–12 μm ribbons exhibited a high permeability of 59,507. Full article

This paper investigates the evolution of the microstructure, mechanical performances, and corrosion resistance of selective laser melting (SLM) 304 steel under different intermittent stretching deformation step sizes, revealing the underlying evolution patterns. The results indicate that the intermittent deformation step size significantly affects the microstructure and performance of SLM 304 steel. Larger step sizes result in more complete molten pool contours, less deformation of grain and cellular structures, and a lower martensite volume fraction; smaller step sizes lead to distorted molten pools, fragmented grains, exacerbated cellular structure distortion, and increased martensite content. In terms of mechanical performances, tensile strength, nano-hardness, and elastic modulus decrease with increasing step size, while elongation increases accordingly. Corrosion resistance improves with larger step sizes, with specimens exhibiting more complete and thicker oxide films on the surface and superior pitting resistance; continuous stretching specimens exhibit the worst corrosion resistance, while the original specimens are the best. Intermittent deformation optimizes properties by regulating microstructure, providing a basis for the design of high-performance SLM 304 steel. This study provides theoretical support for the design and application of additive manufacturing stainless steel components, facilitating the engineering and industrial application of SLM technology in high-end equipment manufacturing. Full article

As a key low-expansion material for high-end equipment such as aerospace and precision instruments, the surface quality of Invar alloy directly determines the operational performance of devices. To fill the research gap in the multi-parameter synergy and mechanism of Invar alloy laser polishing, this study performs polishing experiments on Invar alloy using a burst-mode femtosecond laser, with a repetition rate of 1 MHz and four sub-pulses per burst. The results indicate that energy density plays a dominant role in the polishing effect: with the increase in energy density, the surface roughness first decreases and then increases. A stable molten pool is formed under medium energy density (0.47–0.64 J/cm²), and under the optimal parameter conditions, the surface roughness is reduced to 394 ± 50 nm, representing a 52% reduction compared to the original surface (821 nm). Scanning speed and scanning pitch affect the polishing effect by synergistically regulating energy input: increasing scanning speed under high energy density can inhibit the rise in roughness, while a small scanning pitch can lower the threshold of optimal energy density. Amplitude spectrum analysis reveals that the medium-scale surface undulations are significantly improved after polishing. A four-layer Fully Connected Neural Network (FCNN) model is established to achieve high-precision prediction of polishing effects with a coefficient of determination R² = 0.92, which enables rapid prediction of unknown polishing parameter combinations and provides a new solution path for the optimization of polishing effects. This study clarifies the interaction mechanism between a burst-mode laser and Invar alloy, proposes an efficient ultra-precision polishing method for Invar alloy, and lays a theoretical foundation for its application in the field of high-end manufacturing. Full article

This study investigates the influence of varying positive–negative polarity ratios (EP:EN) on melt pool evolution during alternating current CMT (VP-CMT) arc additive manufacturing through a combined experimental and numerical approach. A multi-layer single-track droplet-melt pool coupling model was established, revealing the regulatory mechanisms governing melt pool flow, temperature distribution, and dimensional changes. These are driven by differences in arc morphology, heat input, and mechanical forces during EP and EN phases. Results indicate that molten pool flow is primarily governed by wire feed, retraction, and Marangoni forces. During the EP phase, arc divergence and elevated heat input result in significantly higher flow velocities than in the EN phase. Molten pool length increases with rising EP proportion, exhibiting periodic dynamic variations. Lateral flow intensity intensifies as EP ratio increases, directly influencing cladding layer morphology. This study provides theoretical basis for optimising additive manufacturing quality by adjusting the EP:EN ratio. Full article

Reliable process monitoring and quality evaluation for resistance spot welding (RSW) have become more important now than ever. An ultrasonic probe embedded into welding electrodes has enabled the acquisition of data about molten pool formation throughout welding, but automation of high-performance ultrasonic data analyses is still necessary to fully realize a monitoring system. This work proposes a two-stage deep learning (DL) approach for automated ultrasonic data analysis for RSW processing monitoring. The first stage conducts semantic segmentation on ultrasonic M-scan welding process signatures, yielding masks for identified molten pool and stack regions from which weld penetration measurements can be directly extracted, as well as expulsion occurrences throughout welding. From input images and segmentation outputs, the second stage directly estimates resultant weld nugget diameters using an additional neural network. Both stages leveraged architectures based on TransUNet, mixing elements of both convolutional neural networks (CNN) and vision transformers, and the effect of cross-attention for stack-up sheet thickness data fusion was investigated via an ablation study. Additionally, in the diameter estimation stage, the ablation study included alternative feature extraction architectures in the network and investigated the provision of M-scans to the model alongside segmentation masks. In both cases, cross-attention was determined to improve performance, and in the case of diameter estimation, providing M-scans as input was found to be beneficial in general. With cross-attention, the segmentation approach yielded a mean intersection over union (IoU) of 0.942 on molten pool, stack, and expulsion regions in the M-scans with 13.4 ms inference time. With cross-attention, diameter estimates yielded a mean absolute error of 0.432 mm with 4.3 ms inference time, representing a significant improvement over algorithmic approaches based on ultrasonic time of flight. Additionally, the approach attained >90% probability of detection (POD) at 0.830 mm below the acceptable diameter threshold and <10% probability of false alarm (PFA) at 0.828 mm above the threshold. These results demonstrate a novel production-ready application of DL in ultrasonic nondestructive evaluation (NDE) and pave the way for zero-defect RSW manufacturing. Full article

The seamless flatness roll is a critical inspection device in cold-rolled strip flatness control systems. Prolonged service causes cracks and scratches on the roll surface, while repeated grinding gradually removes the hardened layer, potentially rendering the roll unusable. To address the risk of thermal damage to internal sensors during the laser cladding repair of seamless flatness rolls, this study proposes a process optimization strategy using the Finite Element Method (FEM) and Response Surface Methodology (RSM). Focusing on an 820 mm roll, a regression prediction model for laser spot and internal component temperatures was constructed using a Box–Behnken design (BBD) based on an experimentally calibrated FEM model. Multi-objective optimization determined the optimal process parameters: laser power of 1.43 kW, laser radius of 3.73 mm, scanning speed of 23.45 mm/s, and overlap rate of 50.40%. Under these conditions, the average error between the predicted and experimental results was only 4.14%. The results confirm that the optimized process ensures the formation of a molten pool while maintaining internal components within safety thresholds, validating the feasibility of this non-destructive repair method. Full article

During the vacuum arc remelting (VAR) process, external convective cooling conditions exert a significant influence on both the heat transfer behavior and solidification microstructure of ingots. In this research, Φ 480 mm IN718 alloy VAR ingots were investigated. A heat transfer model for the VAR mold was established based on the equivalent thermal resistance method to analyze the effects of varying external convective cooling conditions on overall heat transfer performance. Industrial-scale VAR experiments were conducted at different cooling water flow velocities (0.48, 0.73 and 1.30 m/s) to assess how external cooling affects molten pool morphology and microstructure evolution. The results indicate that cooling water flow velocity is the primary factor affecting the heat transfer performance of the VAR mold. Increasing the flow velocity significantly enhances radial heat transfer capability while exerting a relatively limited effect on axial heat transfer. Furthermore, as the cooling water flow velocity increases, the molten pool depth decreases markedly, the pool morphology becomes shallower and more symmetric, and the ingot cooling rate is enhanced. Consequently, dendrite coarsening is effectively suppressed, resulting in a significant reduction in secondary dendrite arm spacing. Specifically, when the flow velocity increases from 0.48 to 1.30 m/s, SDAS decreases by 30.4% at the center, 31.0% at R/2, and 26.5% at the edge, and the SDAS-derived equivalent cooling rate (GR) increases from 6.53–18.25 K/min to 19.41–46.01 K/min across the three representative radial locations. A significant enhancement in the metallurgical quality of the VAR ingot is achieved. Full article

The control of cladding layer morphology is crucial in laser cladding technology. However, traditional process parameter-based regulation suffers from parameter coupling issues, and previous nanosecond laser pretreatment is prone to causing uneven substrate morphology due to significant thermal effects. This study proposes a novel substrate pretreatment method using femtosecond laser etching, employing 45 steel as the substrate and Ni45 powder as the cladding material to investigate its regulatory effect on cladding layer morphology. The results show that femtosecond laser etching enables a good linear correlation between substrate roughness and laser power, forming uniform grid-like microgrooves without the spherical remelted structures observed in nanosecond laser treatment, thus achieving superior regulatory stability. With the increase in substrate roughness, the contact angle and dilution rate of the cladding layer decrease, while the cladding height and width increase, with the optimal cladding quality obtained in the roughness range of 4~7 μm. This study reveals the intrinsic mechanism by which femtosecond laser regulates molten pool behavior through mechanical anchoring and groove guiding effects, providing a more stable technical pathway for the preparation of high-quality cladding coatings. Full article

While extensive research on laser powder bed fusion has focused on optimizing process parameters to improve the performance of manufactured parts, the critical role of effective spatter particle removal in mitigating defects during manufacturing has not received commensurate attention. To address these issues, this study investigates the influence of a key parameter in the atmosphere protection system, namely, airflow velocity, on part performance. Methodologically, a combined approach of numerical simulation and experimental methods was employed to examine in detail the effect of airflow velocity on spatter removal efficiency and its corresponding contribution to the enhancement of formed Inconel 718 part quality. First, Computational Fluid Dynamics–Discrete Phase Model simulations identified an optimal airflow velocity of 0.57 m/s. Subsequently, experimental observations using a high-speed camera system revealed that velocities below 0.6 m/s led to spatter redeposition, resulting in pore and defect formation, whereas velocities exceeding 0.6 m/s increased spatter size and reduced molten-pool stability. The simulation and experimental results are consistent, demonstrating that an appropriate airflow velocity can effectively suppress defects and thereby improve the quality of the fabricated components. This research provides a viable pathway for significantly enhancing the mechanical properties of laser powder bed-fused Inconel 718. Full article

In metal additive manufacturing, the molten pool directly influences the performance of the fabricated components. Therefore, a comprehensive understanding of the molten pool behavior is essential for improving the quality of the parts and mitigating the formation of defects. Selective arc melting (SAM) is a promising additive manufacturing method for fabricating metal matrix composites. However, the melting and solidification process of the powder layer under the arc heat source remains unrevealed. This study aims to elucidate the formation mechanisms of surface morphology during SAM processing and the influence of carbide addition on the melting and solidification behavior of Inconel 718 powder. In this study, thin-walled parts of Inconel 718 and TiC/Inconel 718 composite were fabricated and their microstructures were studied. The melting and solidification behavior of Inconel 718 and TiC/Inconel 718 composite during single-track single-layer deposition was investigated using high-speed photography. Focusing on the differences in the sidewall surface morphology of the Inconel 718 and TiC/Inconel 718 composite parts, the edge feature formation of the deposition track of both materials was studied. Furthermore, the formation mechanism of the differences in forming height at different positions of the deposition track was explored. The results indicate that the melted material in the molten pool of Inconel 718 mainly comes from the mass transport of the beads generated around the molten pool, while the liquid material in the molten pool of TiC/Inconel 718 composite mainly comes from the in situ powder melted under the arc center. During the melting process of Inconel 718 powder, beads at the edge of the heating area come into contact with the boundary of the molten pool and solidify in situ, forming protrusion features. The randomness in the bead size leads to different volumes of molten material at different positions within the same time, thereby causing variations in building height. Full article

This study presents a novel numerical framework that elucidates the critical, yet previously underexplored, role of Marangoni vortex dynamics in determining the final surface quality during the laser polishing of Ti6Al4V (TC4). TC4 titanium alloy is widely used in aerospace, biomedicine, and other high-precision applications due to its excellent specific strength, corrosion resistance, and biocompatibility. However, its surface quality directly affects the fatigue life and service performance of parts, and traditional polishing methods suffer from low efficiency and high pollution. As a non-contact, controllable surface treatment technology, nanosecond laser polishing has demonstrated unique advantages in balancing processing efficiency and surface quality. This study systematically discussed the influence of key process parameters (spot overlap rate, laser power, and scanning times) on the nanosecond laser polishing of TC4 titanium alloy. It revealed the internal physical mechanism by analyzing the temperature and velocity fields and vortex dynamics during molten-pool evolution. It is found that the polishing effect is determined by the process parameters, which adjust the thermal–fluid coupling physical field (temperature distribution, melt flow, and vortex structure) in the molten pool. There is an optimal combination of parameters (spot overlap rate of 79%, laser power of 0.8 W, scanning speed of 5 m/min, scanning 3 times) that can place the molten pool in an optimal dynamic balance state and achieve effective flatness. The experimental results show that, under this parameter, the surface roughness of the specimen with an initial roughness of 1.223 μm is reduced by about 32%. The research further clarified the mechanism by which the initial roughness of the base metal influences the molten pool: the greater the initial roughness, the more pronounced the “peak shaving and valley filling” effect. Under the same parameters, the improvement rate of the specimen with the initial roughness of 1.623 μm could reach about 40%. This study not only establishes the optimized process window but also reveals the essential relationship between “process parameters–bath behavior–surface quality” from the level of the physical field of the molten pool. The findings provide a practical guideline for parameter optimization, directly applicable to the high-precision laser finishing of critical titanium components in the aerospace and biomedical industries. Full article